<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>数组之外找不到弹出undefined</title>
	</head>
	<body>
		<script>
			var cards = [3,4];
			alert(cards[0]);
			alert(cards[1]);
			alert(cards[2]);
		</script>
	</body>
</html>
